1. Field of the Invention
This invention relates to an in-focus state detecting device for use in an auto-focus apparatus or the like.
2. Related Background Art
Heretofore, in an auto focus apparatus, a predetermined in-focus range has been provided and even if the lens is not at the true in-focus position, if the lens is positioned within the in-focus range, it has been detected as being in-focus, thereby stabilizing the detection of the in-focus condition.
As regards the setting of the in-focus range, the greater the range is made, the milder becomes the detection of the in-focus condition and the stabilization of the in-focus state can be achieved while, on the other hand, the accuracy of the in-focus state becomes worse. Accordingly, heretofore, a moderate value has been set from the equilibrium of the stabilization and accuracy of the in-focus state.
Also, the depth of field varies depending on the stop aperture and focal length of the lens and therefore, it has also been proposed to vary the range which can be regarded as in-focus, i.e., the in-focus range, in conformity with the aperture value and the focal length.
Thus, heretofore, the in-focus range has been varied by the stop aperture and the focal length or has been determined with the stabilization of the in-focus state and the accuracy of the in-focus state taken into consideration, but any position the lens is moved to has not been considered at all as a factor which determines said in-focus range and therefore, when the lens is positioned, for example, at the mechanical limit position in the infinity direction, the following inconvenience has occurred.
Even if in a state in which the lens is shifted to the limit position in the infinity direction, it is determined as a result of the focus detection that the lens is not positioned within the in-focus range and the lens is driven in the infinity direction to provide the infocus state of the lens, any further driving of the lens is impossible because the lens is already at said limit position and thus, the focus state can never be improved.
Accordingly, in the case as described above, the indication of the in-focus condition is not effected for any length of time and the photographer may miss a photo opportunity.
As a solution to the above noted problem, it is conceivable that the in-focus range for the result of the focus detection in the state in which the lens has been shifted to the limit position in the infinity direction be set to a greater value than that in the usual case.